Insulating paper



. from eight to ten hours, using Patented June 24, 1930 UNITED STATES OFFICE REED P. ROSE, OF JACKSON HEIGHTS, AND HAROLD E. CUDE, 0F FLORAL PARK, NEW

YORK, ASSIGNORS T0 GENERAL RUBBER COMPANY, OF NEW YORK, N. Y., A COR- rom'rron or NEW JERSEY INSULATING PAPER No Drawing.

This invention relates to improvements in the manufacture of fibrous sheet insulating materials, and particularly to the manufacture of papers for insulating purposes of various' sorts.

The principal object of the invention is to produce a flexible insulating sheet material. Another object is to provide an insulating paper having high dielectric strength, flexibility, surface drag, and tensile strength. A further object is to provide a rapid method of hydrating paper pulp. Another object is to provide an insulating material which may be molded or shaped in any desired form.

The invention comprises beating a paper making fibre to a jelly-like state, combining therewith normally beaten fibre, and making into sheets. The invention includes beating paper making fibre to a jelly-like stage in the presence of chemical reagents. The invention also includes incorporating rubber iglpm any kind of a dispersion with the beaten As one illustration of a method of carrying out the invention, a bleached or unbleached sulphite pulp is employed. Preferably this pulp is cooked according to the Mitscherlich process in which the pulp is cooked slowly at a low temperature in the presence of sulphur dioxide and calcium carbonate. A' quantity of this pulp is placed in a beater and beaten until it has assumed a jelly-like state. Ordinarily this requires a Mitscherlich pulp. Another quantity 0 kraft fibre is beaten separately in accordance with the normal procedure for makin paper. A mixture of 60% by weight- 0 normally beaten kraft and 40% by weight of the elly-like.

product is then made, for instance in the beater in which the jelly-like product has been prepared, and after thorough mixing, is run through the customary paper making operations. If desired that portion of the fibre which is to receive a normal amount of beating may be added directly to the heater in which the other portion of the fibre has already been reduced at least in part to a highly gelatinized condition.

Application filed July 30, 1927. Serial No. 209,636.

The above procedure furnishes a non-porous sheet material having an extremely close formation. The sheet or the paper. possesses a high degree of strength, due to the large percentage of normally beaten fibre present in the sheet. At the same time the presence of the gelatinized fibre serves to close up the interstices in the sheet in a manner which is not possible in ordinary paper. The dielectric strength of this product is considerably greater than that of paper made in the usual way. Sheets and paper prepared by this process can be made on any standard type of paper machinery. For light weights of paper, (for example thicknesses of 0.01

inches) machines of the Fourdrinier and cylinder type may be used and in some cases the Wet machine, While for the heavier weights and in cases where sheets of considerable thickness are desired, very good results may be obtained with a standard Wet machine.

While in the above illustration the per centage of normally beaten kraft has been given as 60%, it is of course understood that this amount may be increased or decreased,

and the percentage of gelatinous fibre decreased 01" increased within fairly wide liniits, depending upon the type of'paper being prepared. Sheet material and paper made in accordance with the above example may or may not contain sizing materials.

Instead of reducing the Mitscherlich pulp to a jelly-like or gelatinous state by a pro- 'tracted beating, the same gelatinous condition may be obtained by beating the pulp for a lesser period of time in the presence of an alkaline substance such as caustic soda or sodium silicate. Suitable proportions are approximately 20 lbs. of sodium silicate to 1000 lbs. of cooked pulp, this giving not more than 2% of silicate on the dry pulp. The pulp is then beaten until it has assumed the gelatinous condition. The amount of time required to reach the desired step of hydration will of course be somewhat dependent upon the type of beater and upon the nature of the pulp selected. WVi'th a fast type of beater and a Mitscherlich sulphite pu p properly prepared, a satisfactory hydration may be obtained after three hrs. of beating.

This gelatinized fibre may be styled chemically hydrated fibre, in contrast with the mechanically hydrated fibre which is obtained by a prolonged beating in the absence of any chemical reagents. This chemically hydrated gelatinous fibre ma be blended with normally beaten pulp a ter the manner of the first example.

In either case, using the mechanically or the chemically gelatinous pulp in admixture with normally beaten pulp, sizing materials, including ordinary rosin size, may be added prior to forming the pulp into sheets, Commercial rosin size may be added to-give say 20 lbs. of rosin per 1000 lbs. of pulp, this requiring approximately 40 lbs. of the commercial size. After this has been thoroughly distributed throughout the beaten pulp, 40 lbs. of'paper makers alum are added to the beater, this amount being suflicient to make the furnish slightly acid. The addition of size and alum are in conformance with standard practice.

Where a high degree of flexibility is required, and at the same time high dielectric strength, it is preferred to add a dispersed rubber to the contents of the beater prior to making into sheets. In case the product is to contain sizing, the rubber dispersion is added before the size is introduced. In the preparation of flexible insulating papers containing dispersed rubber, the following procedure may be utilized. The mixture of normally beaten fibre and gelatinized fibre is prepared in the above described manner, and beating is continued until the proper state of hydration or uniformity of mixture has been reached. The beater roll is then raised off the bed plate. A quantity of rubber latex, sufficient to give 50 lbs. of dry rubber per 1000 lbs. of dry pulp is then added, the contents of the beater having been previously made alkaline. If desired a protective colloid, such as glue, casein and acetylated starch viscose, or their equivalents, etc. may be introduced prior to the addition of rubber, simultaneously therewith or after the rubber dispersion has been added. The beater roll in its elevated position is then continued in rotationand made to serve as a mixing device to distribute the rubber latex throughout the beaten pulp. If size is to be incorporated, it may now be added. After the rubber latex, and the size (if size be used) are thoroughly distributed throughout the, pulp, a dilute solution of a suitable coagulant such as paper makersalum is then slowly and carefully added to the contents of the beater, meanwhile continuing the rotation of the beater roll. By the slow addition ofthe coagulant, the rubber is first agglomerated on the fibres and finally coagulated or anchored thereon. If desired, the coagulant may be added in two stages, in the first of which about twothirds of the total quantity of alum are added slowly, followed by a brief interval of mixing, and then the addition of the, remainder of the alum. With the above proportion of gelatinous pulpcontaining rubber may be made into sheets up to 30-35 points thickness on any of the contlnuous types of paper machines, and thicker sheets may be made onspecial types of machinery, such as the wet machine.

The flexible insulating lpaper thus made contains60% of normally eaten kraft, 40% of gelatinous fibre, and 5 arts of dry rubber per 100 lbs; of pulp. piercing potential of approximately 325 volts per mil. With 80% kraft and 20% jelly the piercing potential is 225 volts per mil. By calendering the aper this value may be increased to 270. The paper is highl flexible, and particularly extensible at t e edges. This property of marginal extensibility is particularly valuable where the paper is to be wound upon aconductor or upon any other his product has a supporting body. By virtue of the marginal I extensibility the paper or sheet material in strip form may be lapped to give tight joints, without tearing at the edges, or wrinkling the strip. Another property possessed by this sheet material may be described as surface drag. When the paper or sheet material is wound upon a conductor or supporting material, the adhesiveness or drag on the surface'of the material makes it possible to wind very tightly, and tends to hold the windings in place, thus eliminating sllppage with the attendant exposure of the conductor. These particular roperties, surface drag and marginal flexibllity, are not possessed by ordinary insulating papers, for these slip, will not wrap tightly, show a tendency to wrinkle or tear at the edges. In fact the ordinary insulating papers cannot be used unless they are held in place by a protect ve coating, usually a braided jacket or its equ1valent.

The presence of the rubber in the insulating papers and sheets serves to increase the wet tensile to a figure which is approximately equal to the wet tensile strength of ordinary insulating paper of the parchment type. By varying the amount of rubber employed, the proportion of normally beaten and elly like pulp, a wide range of mechanical properties, including flexibility, extensibility, tensile strength, tear resistance, folding, etc. may be obtained. .As the proportion of kraft or normally beaten fibre is increased, it will be found that the strength of the paper also increases, but the dielectric strength is reduced. Conversely as the proportion of gelatinous fibre is increased the dielectric strength increases, and the tensile strength decreases somewhat. With greater percentages of rubber the flexibility of the paper is augmented, with but little change in dielectric strength. Wet tensile strength is increased by the inclusion of larger percentages of rubber, and both surface drag and marginal extensibility are increased.

In instances where permanent flexibility is not required, the gelatinous or jelly-like pulp may be used without normally beaten fibre in the production of insulating sheets.

. wise applying, but is not an essential property after the installation, the paper or sheet may be dampened slightly in order to make it suflicientlyflexible during the period of installation, it being understood that upon drying the paper is comparatively brittle.

This product can be molded if desired, and

preferably the moldingis done with the jelly- .like or gelatinous mass after the greater part of the mechanically included water has been removed and most of the shrinkage has taken place. Molded insulating articles made from this pulp can be machined, turned, sawed, drilled, polished, and engraved with a high degree of facility. The cuttings or waste pieces or even the dried powdered product itself may be used in a dry state with or without a binder such as hard wood pitch for packing, or puttying or otherwise filling irregular spaces which are required to be insulated. By so utilizing the dry material it is frequently possible to eflect an economy in the amount of high grade insulating paper which would otherwise be required to secure proper insulating in locationswhich are not easily accessible. c I

The flexibility of the insulating paper' described in the immediately preceding paragraph may be increased by the addition of dispersed rubber. The rocedure forintroducing the rubber may the same as that described for introducing dispersed rubber into mixtures of normally beaten fibre and jelly-like fibre. When rubber-is combined with the gelatinous pulp, an insulating paper may be prepared which has a fair amount of flexibility, sufficient for many purposes, and a high dielectric strength. With 50 lbs. of dry rubber per 1000 lbs. of'dry pulp flexible insulating papers have been made to show a dielectric strength of 1150 volts per mil.

While in the' above illustrations bleached or unbleached sulphite pulp cooked according to the Mitscherlich process has been described, it is understood that instead of the slow Mitscherlich cook, a more rapid cook may be employed in the present invention provided it will give a proper degree of hydration without too greatly impairing the strength of the pulp. Kraft-pulp may be used, but more time is required to hydrate kraft pulp than the above described sulphite pulp. However, kraft pulp is suitable as the source of the fibre which 1s to receive only the normal amount of beating. Vegetable fibres including cotton may be utilized to advantage in the above examples, as one means of securing strong sheets.

The invention contemplates the use of rubber in any of its dispersions, natural, synthetic or artificial, or mixtures of any of these. The rubber itself may comprise the globular rubber particles occurring in natural latex, or it may be an artificial latex comprising dispersed'crude rubber, vulcanized rubber, reclaimed rubber, separately orin admixture with each other, and may include mixtures of these together with other rubberlike gums, etc. Compounding ingredients may be included in the rubber dispersion, and. particularly those ingredients which have the property of imparting or increasing dielectric strength. For example it may be desirable to employ as compounding ingredients certain of the oils, fats, waxes, resins. Vulcanizing materials and accelerators may be added if desired, or the rubbermay be in the form. of a dispersion of vulcanized rubber, that is a vulcanized latex.

In the claims the term dispersed rubber is description of any of the dispersions mentioned in the preceding paragraph. Paper making in redients, without qualification, comprehen s those ingredients which are added to impart special properties to fibrous sheets, as for example waterproofness, flexibility, pliability, denseness, of sheet, etc., and these ingredients include sizing materials in addition as well as special materials which may be added in any suitable form, as solutions or dispersions, or otherwise. Preferably, but not necessarily,such ingredients are added prior to the introduction of the rubber dispersion although they may be combined with the dispersion.

Having thus described our invention, what we claim and desire to protect by Letters Patcm is:

1. A method of making flexible insulating sheet material which comprises hydrating paper making pulp to agelatinous condition, combining normally hydrated pulp therewith, mixing dispersed rubber therewith, and forming into sheets.

2. A method of making flexible insulating sheet material which comprises combining a slowly cooked gelatinized paper making pulp with paper making pulp which, has been hydrated to a considerably less degree, mixing dispersed rubber and paper making in-' gredients therewith, and formin into sheets.

3. A method of making flexib e insulating sheets which comprises hydrating paper making pulp to a gelatinous condition, combining normally hydrated pulp therewith, introducing a protective colloid'and a rubber dispersion thereinto, and forming into sheets.

4. A method of making flexible insulating sheets which comprises hydrating paper making pulp to a gelatinous condition, combining normally hydrated pulp therewith, depositing dispersed rubber thereupon in the presence of'a protective colloid and sizing material, and forming into sheets. I

5. A method of making flexible insulating sheets which comprises hydrating paper making. pulp to a gelatinous state in the presence of an alkaline material, combining normally beaten pulp therewith, mixing dispersed rubher therewith, and making into sheets.

6. A method of making flexible insulating sheets which comprises hydrating paper making pulp to a gelatinous state in the presence of an alkaline material, combining normally beaten pulp therewith, adding sizing material and dispersed rubber thereto, and making into sheets.

7. A method of making "flexible insulating sheets which comprises hydrating paper making pulp-to a gelatinous state in the presence of an alkaline material, combining normally beaten pulp therewith, introducing a protective colloid and a rubber disperslon thereinto, and making into sheets. i

8. A method of making flexible insulating sheets which. comprises hydratin paper making pulp to a gelatinous state in t e presence of an alkaline material, combining nor-v mally beaten. pulp therewith, depositing dis- 4o persed rubber thereupon in the presence of a protective colloid and sizing material, and making into sheets. a i

9. A method of making flexible insulating sheets which comprises converting paper making pulp to a partially gelatinous condition in the presence of an alkaline material,

without greatly decreasing the fibrous strength of the pulp, incorporating dispersed rubber therewith, 1n the presence of aper makingingredients, and forming into s eets.

10. A method of making flexible insulat-' ing sheets which comprises converting paper making pulp to a partially gelatinous connormally beaten pulp, disperse 12. A method of making flexibleinsulating sheets'which comprises converting paper making fibre to a partially gelatinous condiby a close formation, high dielectric strength,

and tensile strength. V

14. Asa new product a flexible insulating sheet material compris'ng normally beaten paper making pulp, gelatinizedpulp, dispersed rubber and sizing material, said sheet being characterized by its marginal extensibihty.

15. An improved insulating material comprising in combination mechanically hydrated paper making fibre, chemically hydratedgelatinized fibre, rubber latex and sizing, said material bein dense, non-porous, and characterized by big dielectric strength 16. A flexible insulating sheet material compcisin in combination chemically hydrated ge atinous paper makin pulp and rubber, a protective colloid, an alkali, and sizing material, said sheet being characterized by close formation, high dielectric strength and tensile strength, great flexibility, particularly at the edges of the sheet, and comparatively high surface drag. I 17. An insulating material comprising rosin sized gelatinized hydrated vegetable fibre, rubber, and a protective colloid including an acetylated starch.

18. An insulating material comprising rosin sized gelatinized hydrated vegetable fibre, rubber, and a protective colloid including an acetylated starch and a soluble silicate.

19. An insulating paper comprising rosin sized highly hydrated cotton fibre, rubber, and a protective colloid including an acetylated ,starch.

20. An insulatingpaper com rising rosin sized highlyhydrated cotton bre, rubber,

and a protective colloid including an acetylated starch and a soluble silicate.

. -21; A method of improving the service qualities of insulating papers of the type containing hydrated vegetable fibres which comprises adding a dispersion of rubber to a hydrated vege able fibre beaten to a gelatinous condition in the presence of a soluble silicate and an acetylated starch,, nixing the rubber with the'fibre, incorporating a paper-' sizing material therewith and forming into sheets. 4

22. A method of improvin the service' qualities of insulating papers 0 the type containing hydrated vegetable fibres which comprises adding a dispersion of rubberto a highly hydrated vegetable fibre beaten in the presence of a soluble silicate and an acetylated starch, mixing the rubber with the fibre,

incorporating a rosin size therewith and forming into sheets.

23. A method of improving the service qualities of insulating papers oft'he type containing hydrated vegetable fibres which comprises adding a dispersion of rubber. to a the fibre, incorporating a rosin size therewith, coagulating the rubber and size upon the beaten fibre with an alum solution, and forming into sheets.

25. A flexible insulating paper comprising an intimate association of highly mechanically and chemically hydrated cellulosic material, paper-sizing, and rubber, said paper being non-hygroscopic, highly resistant to piercing by electric current, and possessing iiigh wet tensile-strength and folding num- 26. A method of improving the useful quality of insulating material of the type consisting of hydrated paper-making fibres which comprises dispersing rubber throughout a suspension of gelatinized mechanically and chemically hydrated paper-making pulp, depositing the rubber on the pulp and forming into a sheet.

27. A method of improving the service qualities of insulating papers of the type containing gelatinized hydrated vegetable fibres which-comprises adding a.dispersion of rubber to a gelatinized hydratedvegetable fire beaten throughout in the,presence of a protective colloid, mixing the rubber with the fibre and forming into sheets.

28. A method of improving the service qualities of insulating papers of the type containing gelatinized hydrated vegetable fibres which comprises adding a dispersion of rubber to a gelatinized hydra-ted vegetable fibre beaten throughout in the presence of a protective colloid, mixing the rubber with 1 the fibre, incorporating a paper-sizing material" therewith and forming into sheets.

29. A flexible insulating paper with high tear "resistance comprising normally hydrated fibre bonded and filled in by a highly hydrated pulp and the deposit from a water dispersion ofrubber.

30. A flexible "insulating paper with high tear resistance comprising normally by drated fibre bonded and filled in by a mechanically and chemically gelatinized pulp, sizing, and the deposit from rubber'latex.

31.-A method of making insulating ma- .terialwhich comprises beating paper pulp and water in the presence of a hydratlng agent until it has assumed a gelatinous state, mixing a water dispersion of rubber there with, uniformly depositing the rubber on the pulp by slow coagulation, and forming an article from the pulp..

32. A method of making insulating material which comprises beating paper pulp in the presence of an alkali until it has assumed a g jatinous state, mixing rubber latex therewith, uniformly depositing the rubber on the pulp by slow coagulation, and forming an article from the pulp.

33. A method of making insulating ma-' terial which comprises beating paper pulp and water in the presence of a hydrating agent until the pulp has assumed 'agelatinous state, mixing the pulp with a water dispersion of rubber and a normally hydrated pulp, depositing the rubber on the pulp by slow coagulation, and forming an article from the pulp.

.34. A method of making insulating materialwhich comprises beating paper pulp in the presence of an alkali until it has assumed a gelatinous state, mixing the pul with rubber latex and a normally hydrate pulp, depositing the rubber on the pulp by slow. coagulation, and forming an article from the pul Signed at ew York, county and State of New York,'this 28th day of July, 1927.

' REED P. ROSE.

Signed at New York, county and State of New York, this 28th day of July, 1927.

HAROLD E. CUDE.

ioo 

